Air pollution is one of _________ (6) proble...

Câu hỏi: Air pollution is one of _________ (6) problems of the current time all over the world. There ___________ (7) a lot of reasons for this pollution. First of all, the release of air pollutants such as smog and solid materials cause air pollution and health issues ___________ (8) human. ___________ (9) dirty wastes in big cities are polluting the whole atmospheric air. Thirdly, motor vehicles are releasing polluted gases contributing to the air pollution. Finally, some natural ________ (10) like dust, soil particles, and natural gases are also the source of air pollution.

A. serious     

B. more serious     

C. the most serious      

D. serious than